On some peculiarities of Vavilov-Cherenkov radiation

Some peculiarities of Vavilov-Cherenkov radiation (VCR) not always given attention are considered. Huygens principle leads in the case of an anisotropic medium to the generalized threshold conditions for the appearance of VCR of a given frequency. The condition for appearance of VCR (and not of a given frequency of radiation) is v = w (w is the group velocity of light). Several peculiarities are observed near the threshold predicted within the elementary theory.     

Use of microorganisms for detection of Vavilov-Cherenkov radiation

The discovery of the photoreactivation effect following irradiation of E. coli cells with ionizing radiation and its experimental and theoretical study has revelated the essential role of Vavilov-Cherenkov radiation in the lethal and mutagenic action of ionizing radiation. It has been shown that the photoreactivation effect in microorganism cells can be successfully used for evaluation of the contribution of the processes of electronic excitation of molecules, being initiated by the Vavilov-Cherenkov radiation and of the direct interaction with secondary electrons, to the biological effects of ionizing radiations.     

On the problem of the unthresholdness of Vavilov-Cherenkov radiation (X)

Angular distributions of radiation occuring at the passing of particles of different velocities through transparent media of different thickness have been calculated in this paper on the basis of various formulae for the intensity of the Vavilov-Cherenkov radiation (VChR) and the optical transitional radiation. In all cases, i.e. at particle velocities both above and below the VChR threshold, the angular distributions are represented as sets of maxima of different orders of K. For particle velocities above the VChR threshold there are maxima with both positive and negative K in addition to the zero (Cherenkov) maximum (K = 0). At velocities below the VChR threshold there are only maxima with positive K in the angular distributions.Comparison of the angular distributions of the radiation calculated by Tamm's formulae (for radiation within the medium) and by Pafomov's formulae (for radiation outside the medium) with the angular distributions of the transitional radiation described by the Ginsburg-Frank formulae has shown that the radiation at velocities below the VChR threshold is also transitional radiation, though not a continuous one (as in the case of particles crossing the boundary of semi-infinite media) but with maxima of different orders.This “transformed” transitional radiation accounts for the unthresholdness effect earlier found by Kobzev and Frank.     

The sagnac effect in optically active media

The propagation of a plane, homogeneous and transverse electromagnetic wave through an optically active medium, at rest in an inertial frame or on a uniformly rotating disc, is studied here. This problem is associated with the well known Sagnac effect. The shift of fringe order one in an interferometer due to the rotation is calculated. The solution of the resulting eigenvalue problem is based on a perturbation technique in which only terms up to the first order in the rotation and the optical activity coefficient are retained.     

Nonlinear effects in media heated by electromagnetic radiation

The features of thermal processes in dielectric absorbing media heated by high-frequency electromagnetic radiation are investigated. It is shown that the temperature dependence of the absorption coefficient of the electromagnetic radiation can result in the development of nonlinear effects: progressive heating in a regime with peaking and localization of the heating region, heating in a regime of lightening of the medium, and formation of quasistationary temperature waves. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 4, pp. 832–838, July–August, 2000.     

Heat propagation by heat conduction in active linear media

A method to use the matrix A-parameter method [1] to solve linear heat-conduction problems in active media is proposed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 4, pp. 739–743, October, 1979.     

Maximum input energy to gas-discharge active media

Fundamental relations are obtained to determine the conditions for utilization of a gas discharge as an active medium to develop lasers with the maximum efficiency. Pis’ma Zh. Tekh. Fiz. 23, 65–67 (May 12, 1997)     

Visibility depth improvement in active polarization imaging in scattering media

A simple image-subtraction technique for further enhancement of the visibility depth in polarized imaging of surfaces immersed in scattering media is proposed and assessed. The technique is based on active illumination with circular or linear polarization states and image detection in the original and the opposite, or orthogonal, states. Contrast enhancement is achieved by subtraction of a fraction of the image recorded in the original state from that recorded in the opposite state. Results demonstrating the effectiveness of this method, obtained with Monte Carlo techniques, show that the visibility depth can be increased by as much as a mean free path. The results obtained are compared with those obtained by use of two alternative methods.     

Ultrasonic tracking of acoustic radiation force-induced displacements in homogeneous media

The use of ultrasonic methods to track the tissue deformation generated by acoustic radiation force is subject to jitter and displacement underestimation errors, with displacement underestimation being primarily caused by lateral and elevation shearing within the point spread function (PSF) of the ultrasonic beam. Models have been developed using finite element methods and Field II, a linear acoustic field simulation package, to study the impact of focal configuration, tracking frequency, and material properties on the accuracy of ultrasonically tracking the tissue deformation generated by acoustic radiation force excitations. These models demonstrate that lateral and elevation shearing underneath the PSF of the tracking beam leads to displacement underestimation in the focal zone. Displacement underestimation can be reduced by using tracking beams that are narrower than the spatial extent of the displacement fields. Displacement underestimation and jitter decrease with time after excitation as shear wave propagation away from the region of excitation reduces shearing in the lateral and elevation dimensions. The use of higher tracking frequencies in broadband transducers, along with 2D focusing in the elevation dimension, will reduce jitter and improve displacement tracking accuracy. Relative displacement underestimation remains constant as a function of applied force, whereas jitter increases with applied force. Underdeveloped speckle (SNR < 1.91) leads to greater levels of jitter and peak displacement underestimation. Axial shearing is minimal over the tracking kernel lengths used in acoustic radiation force impulse imaging and thus does not impact displacement tracking.     

Correlations between the components of stationary radiation in scattering media

Stationary radiation in a radiating, absorbing, and scattering medium is described by linear transport equations, which enables one to represent the radiation intensity as the sum of intensities, each of which is defined by its primary source of radiation and by the transmission of this radiation through the medium. In a scattering medium, the transmission depends on the characteristics of interaction between radiation and matter in the entire volume of the object. Fairly simple general correlations are derived between the intensity components that are independent of the concrete characteristics of the object. Previously, such correlations have only been derived for the case of heat radiation on the basis of the results of analysis of radiation equilibrium in a closed isothermal cavity. In the latter case, the correlations are derived from the condition of stationarity based on the analysis of the equation for the probability of complete disappearance of emerging radiation. The radiation may be arbitrary (it must not necessarily be heat radiation). The object may be of any shape and inhomogeneous. The surrounding walls may be both transparent and nontransparent. External lighting is possible. The correlations include quantities which are subjected to investigations in spectroscopic experiments. The use of the derived correlations in experiments with dust-laden plasma is described.     

Far-field radiation of a vibrating point source in anisotropic media

In this paper, Lamb's technique,⁽¹⁾ which was used to study acoustic radiation due to an external force acting in an infinite isotropic solid or over the surface of an isotropic solid, has been extended to the case of general anisotropic media. The far-field radiation is numerically calculated for a vibrating point source in an infinite anisotropic solid or on the free surface of a semi-infinite anisotropic solid. The directivity patterns of a point source are obtained for the three different elastic modes, and a brief discussion of the main features of the numerical results is presented.     

Thermoelastic destruction of transparent media by laser radiation

It is shown that thermoelastic stresses may be the mechanism for the laser destruction of homogeneous transparent media having high thermal and elastical strength, at least during the initial stage of this destruction. Threshold values of the radiation density required for thermoelastic destruction are calculated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 15, No. 6, pp. 1093–1099, December, 1968.